JP6406482B1 - Trap filter and filter circuit - Google Patents

Abstract

The trap filter (11) includes a first inductor (L1), a second inductor (L2), and a capacitor (C1). The first end (N1) of the first inductor (L1) is connected to the first connection part (T1), and the third end (N3) of the second inductor is connected to the second end (N2) of the first inductor (L1). The fourth end (N4) is connected to the second connection part (T2). The capacitor (C1) is connected in parallel to the second inductor (L2). The first inductor (L1) and the second inductor (L2) are depolarly coupled, and the inductance value of the second inductor (L2) is a mutual relationship generated by the coupling of the first inductor (L1) and the second inductor (L2). It is smaller than the absolute value of inductance.

Description

  The present invention relates to a trap filter for blocking a signal in an unnecessary frequency band and a filter circuit including the same in a high frequency circuit that handles a signal in a high frequency communication frequency band, for example.

  In a high-frequency circuit provided in a mobile phone terminal or the like, a trap filter is used that looks like an equivalent short in a specific frequency band and looks like an equivalent open in other frequency bands.

  For example, Patent Document 1 shows that a trap filter is provided by inserting a simple LC parallel resonant circuit into a signal line.

Japanese Patent Laid-Open No. 2015-29319

  Since a simple LC parallel resonant circuit has a large change in reactance with respect to a frequency change near its resonance frequency, the trap filter including the simple LC parallel resonant circuit has a narrow frequency range showing a short characteristic. Therefore, the stop band is generally narrow.

  In order to widen the stop band of the trap filter, for example, when a plurality of trap filters each having a different stop band are combined, the entire circuit configuration becomes complicated and large.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a trap filter having a wide stop band without complicating the circuit configuration and a filter circuit including the same.

(1) The trap filter of the present application includes a first inductor, a second inductor, and a capacitor. The first inductor has a first end and a second end, and the first end is connected to the first connection portion. The second inductor has a third end and a fourth end, the third end is connected to the second end of the first inductor, and the fourth end is connected to the second connection portion. The capacitor is connected in parallel with the second inductor.

  The first inductor and the second inductor are depolarized (coupled so as to generate a negative mutual inductance), and the inductance value of the second inductor is the mutual inductance generated by the coupling of the first inductor and the second inductor. Less than absolute value.

  In the trap filter of the conventional structure, the change in reactance with respect to the frequency change near the resonance frequency is large, that is, the frequency range in which the reactance is near 0 (= short) is narrow. On the other hand, according to the above configuration, a circuit configuration in which parallel resonance is caused by a series LC circuit of an inductor and a capacitor by mutual inductance and a combined inductance of the second inductor and an inductor by negative mutual inductance. Thereby, the change of the reactance with respect to the frequency change becomes gentler than that of a simple LC resonance circuit, and the frequency band where the reactance is near 0 (= short) is wide. That is, a wide stop band can be obtained.

(2) The inductance of the second inductor is preferably smaller than the inductance of the first inductor. This makes it easy to make the combined inductance of the second inductor and the inductor due to the negative mutual inductance negative. That is, it is not necessary to increase the coupling coefficient between the first inductor and the second inductor so as to increase the absolute value of the mutual inductance.

(3) The resonance frequency of the series LC resonance circuit composed of the inductor by the mutual inductance and the capacitor is single. That is, it does not increase the bandwidth by resonating at two or more different frequencies.

(4) Preferably, the first inductor and the second inductor are configured on a single multilayer substrate, and the capacitor is mounted on the multilayer substrate. This structure reduces the size of the component and reduces the area occupied by the circuit board.

(5) The filter circuit of the present invention includes a band-pass filter connected in series between the first port and the second port, and a trap filter connected to the shunt between the second port and the ground. Is done. The trap filter includes a first inductor, a second inductor, and a capacitor. The first inductor has a first end and a second end, and the first end is connected to the first connection portion. The second inductor has a third end and a fourth end, the third end is connected to the second end of the first inductor, and the fourth end is connected to the second connection portion. The capacitor is connected in parallel with the second inductor.

  The first inductor and the second inductor are depolarized (coupled so as to generate a negative mutual inductance), and the inductance value of the second inductor is the mutual inductance generated by the coupling of the first inductor and the second inductor. Less than absolute value.

  According to the above configuration, a filter circuit having a blocking characteristic over a wide band can be obtained.

(6) Another filter circuit of the present invention is a filter circuit having a plurality of communication frequency band signal ports and filtering a plurality of communication frequency band signals. Then, a trap filter for attenuating a transmission signal band of another communication frequency band is provided in a predetermined port among the signal ports of the plurality of communication frequency bands. The trap filter includes a first inductor, a second inductor, and a capacitor. The first inductor has a first end and a second end, and the first end is connected to the first connection portion. The second inductor has a third end and a fourth end, the third end is connected to the second end of the first inductor, and the fourth end is connected to the second connection portion. The capacitor is connected in parallel with the second inductor.

  The first inductor and the second inductor are depolarized (coupled so as to generate a negative mutual inductance), and the inductance value of the second inductor is the mutual inductance generated by the coupling of the first inductor and the second inductor. Less than absolute value.

  For example, when applied to a front end circuit in a communication circuit corresponding to carrier aggregation that transmits or receives simultaneously in a plurality of frequency bands, the filter circuit is a circuit in which a large number of filters are bundled. In such a filter circuit, according to the above configuration, the transmission signals of other bands can be attenuated by the trap filter.

  According to the present invention, a trap filter having a wide stop band and a filter circuit including the trap filter can be obtained without complicating the circuit configuration.

FIG. 1A is a circuit diagram of the trap filter 11 according to the first embodiment, and FIG. 1B is an equivalent circuit diagram of the trap filter 11. FIG. 1C is a diagram illustrating a connection example of the trap filter 11 to the signal line. FIG. 2A is a diagram illustrating a series LC circuit of an inductor (M) and a capacitor C1, a parallel circuit of an inductor (L2-M), and frequency characteristics of reactance thereof. FIG. 2B is a diagram illustrating an equivalent circuit of the trap filter 11 and frequency characteristics of reactance thereof. FIG. 3A is a diagram showing frequency characteristics of reactance of the trap filter 11 when the trap filter 11 is viewed as a one-port circuit. FIG. 3B is a diagram showing frequency characteristics of insertion loss in a two-port circuit in which the trap filter 11 is connected to the shunt between the signal line and the ground. FIG. 4 is a perspective view of the trap filter 11 according to the second embodiment. FIG. 5 is a schematic diagram showing an internal configuration of the trap filter 11 according to the second embodiment. FIG. 6 is a circuit diagram of the filter circuit 21 according to the third embodiment. FIG. 7 is a diagram showing frequency characteristics of insertion loss of the filter circuit 21 according to the third embodiment. FIG. 8 is a circuit diagram of the filter circuit 22 according to the fourth embodiment. FIG. 9A is a diagram showing frequency characteristics of the series LC circuit of the inductor (M) and the capacitor C1, the parallel circuit of the inductor L3, and the reactance in the trap filter of the comparative example. FIG. 9B is a diagram illustrating an equivalent circuit of a trap filter that is a comparative example, and frequency characteristics of reactance thereof.

  Hereinafter, several specific examples will be given with reference to the drawings to show a plurality of modes for carrying out the present invention. In each figure, the same reference numerals are assigned to the same portions. In consideration of ease of explanation or understanding of the main points, the embodiments are shown separately for convenience, but partial replacement or combination of configurations shown in different embodiments is possible. In the second and subsequent embodiments, description of matters common to the first embodiment is omitted, and only different points will be described. In particular, the same operation effect by the same configuration will not be sequentially described for each embodiment.

<< First Embodiment >>
FIG. 1A is a circuit diagram of the trap filter 11 according to the first embodiment, and FIG. 1B is an equivalent circuit diagram of the trap filter 11. FIG. 1C is a diagram illustrating a connection example of the trap filter 11 to the signal line.

  As shown in FIG. 1A, the trap filter 11 includes a first inductor L1, a second inductor L2, and a capacitor C1. The first inductor L1 has a first end N1 and a second end N2, and the first end N1 is connected to the first connection portion T1. The second inductor has a third end N3 and a fourth end N4, the third end N3 is connected to the second end N2 of the first inductor, and the fourth end N4 is connected to the second connection portion T2. The capacitor C1 is connected in parallel with the second inductor L2.

  The first inductor L1 and the second inductor L2 are coupled so that a negative mutual inductance is generated by coupling. That is, depolarization coupling is performed. The inductance value of the second inductor L2 is smaller than the absolute value M of the mutual inductance generated by the coupling of the first inductor L1 and the second inductor L2. Here, when the inductance of the first inductor L1 is represented by L1, the inductance of the second inductor L2 is represented by L2, and the mutual inductance is represented by M, L1> L2 and L2 <M are satisfied.

  The first inductor L1 and the second inductor L2 coupled to each other are equivalently represented by three inductors as shown in FIG.

  In FIG. 1B, the inductor (L1-M) is an inductor determined by the inductance of the first inductor L1 and the mutual inductance M, and the inductor (L2-M) is the inductance of the second inductor L2 and the mutual inductance M. It is a fixed inductor. The inductor (+ M) is an inductor corresponding to the mutual inductance M. Here, when the inductance of the first inductor L1 is represented by L1, the inductance of the second inductor L2 by L2, and the mutual inductance by M, (L1-M) is a positive inductance and (L2-M) is a negative inductance. is there.

  As shown in FIG. 1B, the trap filter 11 is equivalent to a series LC circuit of an inductor (M) and a capacitor C1 and a parallel circuit of an inductor (L2-M). (L1-M) is a circuit connected in series.

  Since the inductance of the second inductor L2 is smaller than the inductance of the first inductor L1, it is easy to make the combined inductance of the second inductor L2 and the negative mutual inductance -M negative. That is, it is not necessary to increase the coupling coefficient between the first inductor L1 and the second inductor L2 so as to increase the absolute value of the mutual inductance.

  As shown in FIG. 1C, the trap filter 11 is connected to the shunt between the signal line and the ground.

  Hereinafter, characteristics of the trap filter 11 will be described using an equivalent circuit diagram of the trap filter 11.

  FIG. 2A is a diagram showing the above-described series LC circuit of the inductor (M) and the capacitor C1, the parallel circuit of the inductor (L2-M), and the frequency characteristics of the reactance. FIG. 2B is a diagram illustrating an equivalent circuit of the trap filter 11 and frequency characteristics of reactance thereof. Here, each element constant is as follows.

L1 = 7.5nH
L2 = 1.3nH
C1 = 3.5pF
M ≒ 2.5nH (coupling coefficient k = 0.8)
In FIG. 2A, in the frequency range FR11, the reactance of the capacitor C1 is large, and therefore, the reactance of the inductor (L2-M) is dominant. In this frequency range, the reactance of the parallel circuit is almost zero.

  In FIG. 2A, the frequency range FR12 is a range where the reactance of the series LC circuit of the inductor (M) and the capacitor C1 is dominant. That is, as the frequency increases, the reactance of the parallel circuit increases in the positive direction.

  In FIG. 2A, the frequency range FR2 is a range in which the positive reactance by the series LC circuit of the inductor (M) and the capacitor C1 and the negative reactance by the inductor (L2-M) balance (resonate in parallel). In this range, no current flows between both ends of the parallel circuit.

  In FIG. 2A, the frequency range FR30 is a range in which the reactance of the inductor (M) increases and the negative inductance component due to the inductor (L2-M) is dominant. That is, the reactance stays in the negative range, and the reactance becomes more negative as the frequency increases.

  In FIG. 2B, the frequency range FR10 is a range in which characteristics mainly due to the inductance of the inductor (L1-M) appear. That is, the reactance of the trap filter 11 increases in the positive direction as the frequency increases.

  In FIG. 2B, the frequency range FR2 is based on the positive reactance by the series LC circuit of the inductor (M) and the capacitor C1 and the inductor (L2-M), similarly to the frequency range FR2 shown in FIG. This is a range in which negative reactance balances (resonates in parallel).

  In FIG. 2B, the frequency range FR31 is a trap filter as a result of adding a positive inductance due to the inductor (L1-M) to a negative inductance component due to the dominant inductor (L2-M) in the parallel circuit. This is a range in which the reactance of 11 is near zero. This frequency range acts as a stop band.

  In FIG. 2B, the frequency range FR32 is a range in which the characteristic due to the combined inductance of the inductors (L1-M), (L2-M), and (M) appears. That is, the reactance of the trap filter 11 increases in the positive direction as the frequency increases.

  Here, the characteristics of the trap filter to be compared will be exemplified.

  FIG. 9A is a diagram showing frequency characteristics of the series LC circuit of the inductor (M) and the capacitor C1, the parallel circuit of the inductor L3, and the reactance in the trap filter of the comparative example. The inductance of the inductor L3 is positive. FIG. 9B is a diagram illustrating an equivalent circuit of a trap filter that is a comparative example, and frequency characteristics of reactance thereof. This trap filter is a circuit in which an inductor (L1-M) having a positive inductance is connected in series to the parallel circuit shown in FIG. Here, each element constant is as follows.

L1 = 7.5nH
L3 = 1.2nH
C1 = 3.5pF
M ≒ 2.5nH
In FIG. 9A, the frequency range FR30P is a range in which mainly the inductance component of the inductor L3 is dominant. That is, as the frequency increases, the reactance of the parallel circuit increases in the positive direction. In FIG. 9A, a range corresponding to the frequency range FR30 shown in FIG.

  In FIG. 9B, the frequency range FR31P is a range where the reactance of the trap filter of the comparative example is near zero. This frequency range acts as a stop band.

  Since the inductance of the inductor L3 is positive in the trap filter of this comparative example, the characteristic that the reactance tends to be negative due to the action of the negative inductor (L2-M) in the trap filter 11 of the present embodiment does not appear. That is, when the inductor L3 and the inductor (M) in the parallel circuit have the same sign, there is no exchange of energy, and there is no frequency range in which the negative inductance increases in the parallel circuit. Therefore, in the trap filter of this comparative example, the frequency range in which the reactance is near 0 is narrow. In FIG. 9B, a range corresponding to the frequency range FR31 shown in FIG.

  FIG. 3A is a diagram showing frequency characteristics of reactance of the trap filter 11 when the trap filter 11 is viewed as a one-port circuit. FIG. 3B is a diagram showing frequency characteristics of insertion loss in a two-port circuit in which the trap filter 11 is connected to a shunt between the signal line and the ground.

  3A and 3B, the solid line indicates the characteristics of the trap filter 11, and the broken line indicates that the negative inductor (L2-M) in the trap filter 11 is replaced with a positive capacitor (negative reactance is expressed by a capacitor). It is a characteristic of the trap filter of a comparative example. The capacitance of the positive capacitor is determined so that the parallel resonance frequency of the trap filter of this comparative example matches the parallel resonance frequency of the trap filter 11 of the embodiment.

  As shown in FIG. 3A, the trap filter 11 of the present embodiment has a reactance of 0 at the frequency fa, and a band rejection having the frequency fa as the center frequency as shown in FIG. 3B. A characteristic appears. The trap filter of the comparative example has a reactance of 0 at the frequency fb as shown in FIG. 3A, and a band rejection characteristic with the frequency fb as the center frequency as shown in FIG. 3B. appear.

  Compared to the comparative example, the trap filter 11 of the present embodiment has a wider frequency range in which the reactance is close to 0, and therefore has a wider stopband. In addition, as compared with the comparative example, the trap filter 11 of the present embodiment has a frequency range in which the reactance is close to 0 away from the parallel resonance frequency fo. Since the frequency characteristic of the trap filter resistance is maximized at the parallel resonance frequency and becomes smaller as the distance from the parallel resonance frequency increases, the frequency range in which the reactance is near 0 is away from the parallel resonance frequency fo as described above. Therefore, the resistance in the frequency range FR31 is small. Therefore, the attenuation in the frequency range FR31 is larger than that of the comparative example.

  As described above, the trap filter 11 of the present embodiment has a wider stop band and a larger attenuation than a conventional simple LC parallel resonant circuit.

  In the trap filter 11 of the present embodiment, the resonance frequency of the series LC resonance circuit composed of the mutual inductance M and the capacitor C1 is single. That is, the trap filter 11 does not have a wide band by providing a plurality of resonance circuits that resonate at two or more different frequencies, so it can be configured with a small number of elements, and can be reduced in size and area occupied. .

<< Second Embodiment >>
In the second embodiment, a trap filter configured as a single component will be described. FIG. 4 is a perspective view of the trap filter 11 of the present embodiment, and FIG. 5 is a schematic diagram showing an internal configuration thereof.

  The trap filter 11 includes a multilayer substrate 10 and a chip capacitor C1 mounted on the multilayer substrate 10. In the multilayer substrate 10, the first inductor L1 and the second inductor L2 shown in FIG. 1A are formed. In addition, mounting terminals T <b> 1 and T <b> 2 are formed on the lower surface of the multilayer substrate 10. Pads for connecting the chip capacitor C1 are formed on the upper surface of the multilayer substrate 10, and the chip capacitor C1 is connected to these pads.

  As shown in FIG. 5, the coil conductor pattern constituting the first inductor L1 and the coil conductor pattern constituting the second inductor L2 are formed in the multilayer substrate 10. All the coil conductor patterns are helical and are arranged coaxially.

  According to the present embodiment, the trap filter 11 can be surface-mounted on the circuit board as a single component. In addition, since the components can be reduced in size, the area occupied by the circuit board is also small.

  The capacitor C1 may be integrated by forming an electrode constituting the capacitor C1 in the multilayer substrate 10. Further, a chip capacitor constituting the capacitor C <b> 1 may be embedded in the multilayer substrate 10.

<< Third Embodiment >>
In the third embodiment, an example of a filter circuit including the trap filter 11 shown in the first and second embodiments is shown.

  FIG. 6 is a circuit diagram of the filter circuit 21. The filter circuit 21 includes a band pass filter BPF connected in series between the first port P1 and the second port P2, and a trap filter 11 connected to a shunt between the second port P2 and the ground. Composed. The trap filter 11 is the trap filter 11 shown in the first and second embodiments. The band pass filter BPF is, for example, a SAW filter.

  FIG. 7 is a diagram showing the frequency characteristics of the insertion loss of the filter circuit 21 of the present embodiment. In FIG. 7, the solid line indicates the characteristic of the filter circuit 21 of the present embodiment, and the broken line indicates the characteristic of the filter circuit when the trap filter 11 is not provided.

  In FIG. 7, the passband characteristic centered on 2.15 GHz depends on the characteristic of the bandpass filter BPF shown in FIG. Moreover, the attenuation characteristic of 2.5 GHz or more and 2.85 GHz or less depends on the characteristic of the trap filter 11 shown in FIG.

  The filter circuit 21 shown in FIG. 6 is used, for example, in a portion that passes a reception signal of a predetermined band, and can greatly attenuate unnecessary transmission signals that wrap around.

  Note that the SAW filter and the trap filter 11 constituting the bandpass filter BPF shown in FIG. 6 may be integrated into a single component. For example, as shown in FIGS. 4 and 5, the first inductor L1 and the second inductor L2 may be configured on a multilayer substrate, and the capacitor C1 and the SAW filter chip may be mounted on the multilayer substrate.

<< Fourth Embodiment >>
The fourth embodiment shows an example of a filter circuit including the trap filter 11 shown in the first and second embodiments.

  FIG. 8 is a circuit diagram of the filter circuit 22 according to the fourth embodiment. The filter circuit 22 is a front-end circuit connected between the antenna ANT and the transmission / reception circuit. The filter circuit 22 includes diplexers DIP1, DIP2, and DIP3, RF switches SW1 and SW2, a number of bandpass filters F, and trap filters 11A, 11B, 11C, 11D, and 11E. In this example, the trap filter 11A is connected to the subsequent stage of the diplexer DIP1, and the trap filter 11B is connected to the subsequent stage of the diplexer DIP3. The trap filters 11C, 11D, and 11E are connected to output ports (reception ports) Rx1, Rx2, and Rx4 of received signals, respectively.

  The filter circuit 22 is applied to a communication circuit corresponding to carrier aggregation that transmits or receives simultaneously in a plurality of frequency bands. The filter circuit 22 is a circuit in which a large number of filters are bundled. In such a filter circuit, the trap filter 11 attenuates a transmission signal of another band (the power of the sneak transmission signal) different from the reception signal of the communication band using the reception port.

<< Other embodiments >>
In the embodiment described above, the first inductor L1 and the second inductor L2 are configured on the multilayer substrate, and the capacitor C1 and the SAW filter chip are mounted on the multilayer substrate. However, a duplexer or the like is mounted on the multilayer substrate. A composite filter or a circulator may be mounted to form a single part.

  Finally, the description of the above embodiment is illustrative in all respects and not restrictive. Modifications and changes can be made as appropriate by those skilled in the art. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention includes modifications from the embodiments within the scope equivalent to the claims.

ANT ... antenna BPF ... band pass filter C1 ... capacitors DIP1, DIP2, DIP3 ... diplexer F ... band pass filter L1 ... first inductor L2 ... second inductor L3 ... inductor M ... mutual inductance N1 ... first end N2 ... second end N3 ... 3rd end N4 ... 4th end P1 ... 1st port P2 ... 2nd port SW1, SW2 ... RF switch T1 ... 1st connection part T2 ... 2nd connection part 10 ... Multilayer board 11, 11A, 11B, 11C, 11D, 11E ... Trap filters 21, 22 ... Filter circuit

Claims (6)

A first inductor having a first end and a second end, wherein the first end is connected to a first connection;
A second inductor having a third end and a fourth end, wherein the third end is connected to the second end of the first inductor, and the fourth end is connected to the second connection portion;
A capacitor connected in parallel to the second inductor;
With
The first inductor and the second inductor are depolarized and coupled,
The inductance value of the second inductor is smaller than the absolute value of the mutual inductance generated by the coupling of the first inductor and the second inductor.
Trap filter.   The trap filter according to claim 1, wherein an inductance of the second inductor is smaller than an inductance of the first inductor.   The trap filter according to claim 1 or 2, wherein a resonance frequency of a series LC resonance circuit including the mutual inductance and the capacitor is single.   4. The trap filter according to claim 1, wherein the first inductor and the second inductor are configured on a single multilayer substrate, and the capacitor is mounted on the multilayer substrate. 5. A band pass filter connected in series between the first port and the second port, and a trap filter connected to the shunt between the second port and the ground,
The trap filter is
A first inductor having a first end and a second end, wherein the first end is connected to a first connection;
A second inductor having a third end and a fourth end, wherein the third end is connected to the second end of the first inductor, and the fourth end is connected to the second connection portion;
A capacitor connected in parallel to the second inductor;
With
The first inductor and the second inductor are depolarized and coupled,
The inductance value of the second inductor is smaller than the absolute value of the mutual inductance generated by the coupling of the first inductor and the second inductor.
It is characterized by
Filter circuit. A filter circuit having a plurality of communication frequency band signal ports and filtering the plurality of communication frequency band signals;
A predetermined port among the plurality of communication frequency band signal ports includes a trap filter that attenuates a transmission signal band of another communication frequency band,
The trap filter has a first end and a second end, and the first inductor is connected to the first connection portion;
A second inductor having a third end and a fourth end, wherein the third end is connected to the second end of the first inductor, and the fourth end is connected to the second connection portion;
A capacitor connected in parallel to the second inductor;
With
The first inductor and the second inductor are depolarized and coupled,
The inductance value of the second inductor is smaller than the absolute value of the mutual inductance generated by the coupling of the first inductor and the second inductor.
It is characterized by
Filter circuit.

Images